The present invention relates to circle drawbar assemblies of the type used in motorgraders.
Motorgraders have a drawbar assembly attached near the nose of the grader and the drawbar assembly is pulled by the grader as it moves forward. The drawbar rotatably supports a circle member at a free end of the drawbar and the circle member supports a work implement. The angle of the work implement beneath the drawbar is changed by rotation of the circle member relative to the drawbar. In addition, hydraulic cylinders attached to the grader frame are used to position the circle drawbar assembly beneath the grader frame.
Traditionally, circle members are supported by a series of bearings attached to the drawbar and the circle member includes a series of gear teeth disposed to the exterior circle member or disposed to the interior of the circle member. These gear teeth cooperate with one or more drive gears associated with drive motors attached to the drawbar. Other arrangements have used pinion gears which mesh with the large ring gear. In one design, hydraulic cylinders are used in association with a crank arm for rotating of the pinion gears.
The manufacture of the large ring gear is time consuming and expensive. Some designs have been directed to more effective ways for manufacture of this gear component by breaking the ring gear into smaller segments attached to the rotatable circle. This design has some advantages and disadvantages, however, it is still time consuming and expensive to manufacture.
A motorgrader has high loads exerted on the work implement typically a grader blade secured beneath the grader. The ring gear and pinion gears or the drive motors are subject to high loads as these components are used to lock the circle member in the set position. In addition to the high load environment, the very nature of a motorgrader exposes these components to abrasive contaminants. Work hardening of the components and other heat treatment techniques are used, however, the components are subject to wear. Unfortunately, in many applications it is highly desirable to closely control the position of the grader blade which is difficult when wear is present.
There remains a need for an efficient manner of controlling the locking and movement of a circle member in a circle drawbar assembly.
A circle drawbar assembly for use in a motorgrader, according to the present invention comprises a drawbar frame, a circle member mounted on the drawbar frame for rotation about a circle axis, a work implement mounted below the circle member and rotatable therewith, a drive arrangement secured to the frame and connected to the circle member for rotation thereof about the circle axis. The drive arrangement comprises a plurality of hydraulic cylinders connected to the circle member at space positions and each hydraulic cylinder is pivotally connected to the frame at a position adjacent to but offset from the circle axis. A control arrangement is used for controlling the extension and retraction of the cylinders in timed relationship to rotate the circle member about the circle axis.
According to an aspect of the invention the control arrangement is a hydraulic timing valve.
According to yet another aspect of the invention the timing valve includes an input signal corresponding to the rotary position of the circle member.
In yet a further aspect of the invention the timing valve includes a mechanical input signal associated with the rotary position on the circle member relative to the drawbar frame, and the mechanical input signal is used to control the hydraulic cylinders.
In a further aspect of the invention the plurality of hydraulic cylinders are at least three hydraulic cylinders.
In a further aspect of the invention the drive arrangement can be used to effect rotation of the circle member through an angle of at least 270 degrees.
In yet a further aspect of the invention the cylinders are attached to the circle member to define a similar angular spacing between adjacent cylinders.
In a further aspect of the invention the drawbar member has at least three bearings secured thereto which engage an inwardly directed flange of the circle member.
In a further aspect of the invention the hydraulic cylinders function to maintain the position on the circle member when the cylinders are not used to rotate the circle member.
In a further aspect of the invention the circle member includes at an outer edge thereof, a downwardly extending circle flange connected to said inwardly extending flange and being concentric therewith.